This invention relates to a method of and apparatus for sealing a color cathode-ray tube, and more particularly to a method of and apparatus for sealing a color cathode-ray tube used for the process of sealing the electron gun assembly of a color cathode-ray tube.
A color cathode-ray tube comprises a funnel-shaped glass bulb with a panel, or a vacuum envelope, and an in-line electron gun assembly inserted in the neck of the bulb in such a manner that it is held in a specific position. FIG. 1 shows a color cathode-ray tube obtained after the electron gun assembly 12 has been inserted in the bulb 11 and the bulb has been sealed.
In such a color cathode-ray tube, when the electron gun assembly 12 that generates three electron beams for RGB, or red, green, and blue, is sealed, it is desirable that an imaginary line X--X passing through the center of each of three electron beam holes 12r, 12g, and 12b made in an electron gun electrode 12a shown in FIG. 2 should be aligned with an imaginary line (a reference line in a horizontal plane) H--H in the direction of the major axis passing through the center of a rectangular screen of the bulb 11 shown in FIG. 1. FIG. 4 shows a state where imaginary line X--X does not align with imaginary line H--H and crosses the latter at an angle of .theta., or a misaligned state in a twisted manner.
For monitors used with the recent personal computers, the standard for rotation known as twist has become severer.
Imaginary line X--X and imaginary line H--H do not exist in reality. Therefore, in actual adjustment, imaginary line H--H is defined as a parallel line to a pad face 13 of the bulb 11 shown in FIG. 1 and imaginary line X--X is determined using one side face in the direction of the major axis of the electron gun assembly 12 of FIG. 2 as a reference face. The electron gun assembly 12 is provided in the neck of the bulb 11 in such a manner that imaginary line H--H aligns with imaginary line X--X. Then, the air is exhausted from the bulb 11. Thereafter, the neck is sealed.
A method of assembling a color cathode-ray tube by providing such an electron gun assembly 12 in the bulb 11 has been disclosed in, for example, Jpn. Pat. Appln. KOKOKU Publication No. 61-20106. In the assembly, the position of the electron gun assembly 12 is determined as described below in detail and provided in the neck.
As shown in FIG. 1, an electron gun electrode 12a shown in FIG. 2 is connected electrically and mechanically to a stem section 16 with stem pins 15 provided in the lower part, forming an electron gun assembly 12, which is provided in the bulb 11. Specifically, as shown in FIG. 3, the electron gun electrode 12a is provided on the stem section 16 in such a manner that imaginary line X--X passing through three electron beam holes 12r, 12g, and 12b made in the electron gun electrode 12a crosses, at right angels, imaginary line Y--Y passing through a pair of top and bottom stem pins 15a, 15a serving as a reference. When the electron gun electrode 12a is connected to the stem section 16, it is ideal that imaginary line X--X should cross imaginary line Y--Y accurately at right angles. In actual assembly, however, there arises a small twist error.
The position of the electron gun assembly 12 put together as described above is measured and inserted in the bulb 11. When the electron gun assembly 12 is inserted in the bulb 11, the electron gun assembly 12 is placed in a specific position. In the positioning, a pair of square holes 14, 14 made in both side faces of the electron gun electrode 12a, one hole in each face is used. Specifically, a laser beam is emitted from one side of the pair of square holes 14, 14 and pass through the square holes. Then, the diffraction images of the square holes 14, 14 are sensed. When the diffraction images form a specific pattern, the electron gun assembly 12 is so set that it has a specific location with respect to the screen. Thereafter, the neck in which the electron gun assembly 12 has been provided is sealed.
In the method disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 61-20106, an electron gun assembly 12 with a pair of square holes 14, 14 in both side faces of an electron gun electrode 12a is mounted on a rotating adjustment table (not shown) as shown in FIG. 2. The rotating adjustment table can rotate on the center axis Z--Z of the bulb 11 combined with the electron gun assembly 12 and is so set that it has a specific positional relationship with a holding unit (not shown) for holding the bulb 11.
Next, a laser beam is generated in such a manner that the center axis Z--Z crosses the direction of optical axis at right angles. The laser beam is emitted from one side of the pair of square holes 14, 14. The laser beam passes through the pair of square holes 14, 14 and is projected on a sensor (not shown). The sensor monitors the diffraction pattern formed as a result of the laser beam passing through the square holes 14, 14. The diffraction images are displayed on a monitor television. Then, the rotating adjustment table is manually rotated until the displayed diffraction images have formed a specific image, thereby adjusting the angle of the electron gun assembly 12.
Thereafter, the bulb 11 is so held by the holding unit that imaginary line H--H of the bulb 11 is placed in a specific position at which line H--H aligns with the optical axis of the laser beams. In this state, the electron gun assembly 12 is inserted in the neck of the bulb 11 as shown in FIG. 1. Thereafter, the electron gun assembly 12 is sealed in the bulb 11 by a burner (not shown).
In such an assembly method, the aligning of the direction of rotation of the electron gun assembly 12 is done by the operator who turns the adjusting screw serving as the driving mechanism of the rotating adjustment table, while watching a monitor television. Therefore, the result of adjustment varies greatly, depending on the operator. Consequently, it is difficult to seal the electron gun assembly 12 with high accuracy.